Open-circuit Flux Linkage Research Articles

Analysis of mechanical flux-weakening by using the end-cap of the switched flux permanent magnet machines

PurposeThe purpose of this study is to develop a novel mechanical flux-weakening topology for the switched flux permanent magnet (SFPM) machine to extend the speed range, which will be suitable for the electric vehicles and hybrid electric vehicles.Design/methodology/approachThe 3 dimensional mechanical flux-weakening model with flux adjusters (FAs) in the end-cap is established. Subsequently, the electromagnetic performance is compared between the SFPM machine with FAs in the end-cap and without FAs. The open circuit flux-linkage is calculated by finite element analysis (FEA) to investigate the influence of this mechanical flux-weakening topology together with the d/q-axis inductance. The flux-weakening capability and torque-speed curve is also calculated.FindingsThe proposed topology decreases the permanent magnet flux-linkage and increases the d-axis inductance, which improve the flux-weakening capability simultaneously. Subsequently, the speed range and constant power region are much wider than those without FAs. Finally, the prototype is fabricated and the measured result of the open circuit back electromotive force has good agreement with the FEA result.Originality/valueThis paper provides a novel mechanical flux-weakening topology with FAs in the end-cap for the SFPM machine, whose volume is smaller than another mechanical flux-weakening topology with FAs at the stator outside. Thus, higher torque and power density can be obtained compared with the SFPM machine with FAs at the stator outside.

Analytical Airgap Field Model and Experimental Validation of Double Sided Hybrid Excited Linear Flux Switching Machine

Linear Flux Switching Machines (LFSMs) are suitable candidates for long stroke applications as they confines all excitation sources to primary thus leaving completely passive, robust, and low cost secondary. Permanent Magnet LFSMs (PMLFSMs) enables high thrust force density and efficiency. However, deficiency of controllable air-gap flux, risk of PM demagnetization, and increasing cost of rare earth PM materials diverted researchers towards Field Excited LFSMs (FELFSMs). FELFSMs wiped out aforementioned PMLFSM’s shortcomings at the cost of low thrust force density. In this paper, merits of PMLFSM and FELFSM are combined by proposing a novel Hybrid Excited LFSM (HELFSM). Proposed machine is excited by PMs, Field Excitation Coils (FECs), and Armature Windings (AWs). However, complex magnetic circuit of poly-excited HELFSM compels designers to adopt FE Analysis (FEA) for design, analysis, and optimization. To decrease dependency on computationally complex and time consuming FEA, an analytical model combining lumped parameter magnetic equivalent circuit, Fourier analysis, Laplace equation, and Maxwell Stress Tensor method is proposed to predict open-circuit flux linkage, B-EMF, normal and tangential components of no-load and on-load magnetic flux density, detent, and thrust force performance. Finally, predictions of the developed analytical model are validated with corresponding FEA and experimental results.

Analytical Sub-Domain Model for Magnetic Field Computation in Segmented Permanent Magnet Switched Flux Consequent Pole Machine

Computational complexity, magnetic saturation, complex stator structure and time consumption due to repeated iteration compels researchers to adopt alternate analytical model for initial design of electric machines especially Switched Flux Machine (SFM). To overcomes the abovesaid demerits, In this article alternate analytical sub-domain model (SDM) for magnetic field computation in Segmented PM switched flux consequent pole machine (SPMSFCPM) with flux bridge and flux barriers accounting boundary and interface conditions, radial magnetized PMs (RM-PMs) and circumferential magnetized PMs (CM-PMs), interaction between stator slots and inner/outer rotor topologies is proposed. Overall field domain is divided into air gap, stator slots and Permanent Magnet (PM) accounting influence of CM/RM-PMs under no-load and on-load conditions. Analytical expression of field domain is obtained by solving magnetic vector potential utilizing Maxwell’s equations. Based on the magnetic field computation especially no-load and on-load condition, Magnetic Flux Density (MFD) components, open-circuit flux linkage, mechanical torque and cogging torque are computed utilizing Maxwell Stress Tensor (MST) method. Moreover, developed analytical SDM is validated with globally accepted Finite Element Analysis (FEA) utilizing JMAG Commercial FEA Package v. 18.1 which shows good agreement with accuracy of ~98%. Hence, authors are confident to propose analytical SDM for initial design of SPMSFCPM to suppress computation time and complexity and eliminate requirements of expensive hardware and software tools.

Analysis of Rotor Poles and Armature Winding Configurations Combinations of Wound Field Flux Switching Machines

The general rules of rotor pole and armature winding configurations combinations for 24-slot stator wound field flux switching machines (SWFFSMs) are investigated thoroughly in this article. Meanwhile, based on the virtual coil method, a novel general auxiliary evaluation variable, which is proportional to the fundamental amplitude of open-circuit flux-linkage of armature coil is proposed in this article. Hence, these SWFFSMs with larger open-circuit flux-linkage and back-EMF can be obtained effectively. In addition, the effect of rotor poles on the complementarity of armature windings is analyzed so that more sinusoidal and symmetrical back-EMF can be acquired. Furthermore, for these SWFFSMs with larger open-circuit back-EMF, the torque capability is restricted to a considerable extent due to the deep magnetic saturation caused by overlapping armature winding. Hence, a new method by optimizing the ratio of armature slot area and excitation slot area is proposed in this article to ensure that the higher torque density of selected SWFFSMs can be maintained. To verify the validity of analysis and methodology proposed in this article, seven representative SWFFSMs are chosen for verification at no load by the finite-element analysis (FEA) while a 24s/17p SWFFSM with the highest torque density is chosen for further verification at on-load conditions by the FEA and experiments.

Analysis and Design of Novel High Speed Permanent Magnet Machine Considering Magnet Eddy Current Loss

In high speed permanent magnet (HSPM) machines, the computation of magnet eddy current loss is essential as these losses significantly affect the temperature of the permanent magnet (PM) and electromagnetic performance and can result in irreversible demagnetization of the PM. Several techniques have been adopted to minimize the eddy current loss of the PM; however, superior performance has not been achieved yet. In this paper, the design characteristics of the HSPM machine are analyzed. The PM is covered by a titanium sleeve to retain the PM on the rotor and to further reduce the eddy current loss of the magnet. The undesirable harmonics of the airgap flux density are minimized, which reduces the eddy current loss in the solid PM and rotor. Two existing models, with and without auxiliary slots, are examined and compared with the proposed design having a titanium-based retaining sleeve. The analysis reveals that the eddy-current loss, cogging torque, and iron losses of the PM are reduced by 82%, 73%, and 44.7%, respectively, in the proposed model; however, a marginal increase is observed in the average rated torque profile and open circuit flux linkage.

Analytical Modelling of Open-Circuit Flux Linkage, Cogging Torque and Electromagnetic Torque for Design of Switched Flux Permanent Magnet Machine

Magnetic saturation and complex stator structure of Switched Flux Permanent Magnet Machine (SFPMM) compels designers to adopt universally accepted numerical method of analysis i.e. Finite Element Analysis (FEA). FEA is not preferred for initial design due to its computational complexity and is time consuming process because of repeated iterations. This paper presents an accurate analytical approach for initial design of proposed twelve-stator-slot and ten-rotor-tooth (12/10) with trapezoidal slot structure SFPMM. Air-gap Magnetic Equivalent Circuit (MEC) models with Global Reluctance Network (GRN) methodology is utilized for calculation of open-circuit flux linkage. Fourier Analysis (FA) for cogging torque, and Maxwell Stress Tensor (MST) method for electromagnetic torque where radial and tangential components of the air-gap flux density are produced by the currents flowing in three phase armature winding. Analytical predictions are validated by FEA utilizing JMAG software and shows errors less than ~2% for open-circuit flux linkage, ~4.2% for cogging torque, and ~2% for average electromagnetic torque.

Demagnetization Withstand Capability Enhancement of Surface Mounted PM Machines Using Stator Modularity

The flux gaps in alternate stator teeth of the modular permanent-magnet machines can have a significant impact on the total magnet flux density, and hence the potential magnet reversible/irreversible demagnetization under flux weakening operations or short-circuit conditions. Such a problem has not been studied in literature and will be investigated in this paper. The influence of flux gaps on the d -axis inductance and the potential peak short-circuit current is analyzed for different slot/pole number combinations. It is found that the flux gaps will affect both d -axis inductance and open-circuit flux linkage, and hence reduce short-circuit current of machines with pole number (2 p ) smaller than slot number ( Ns ), while they will increase the short-circuit current of machines with 2 p > Ns . However, the opposite phenomena can be observed for demagnetization withstand capability. For machines having 2 p , the flux gaps tend to lower withstand capability, while for machines having 2 p > Ns , this capability can be improved. Other parameters such as magnet thickness and temperature have also been accounted for in the demagnetization analysis. Tests have been carried out to validate the predictions of inductances and short-circuit current, as well as performance such as phase back electromotive force, cogging torque, and static torque for machines with one defective magnet, which represents the case of partially demagnetized magnets.

Influence of stator/rotor‐pole combination on electromagnetic performance in all/alternate poles wound partitioned stator doubly salient permanent magnet machines

In this paper, the influence of stator/rotor pole combinations on electromagnetic performance in partitioned stator (PS) doubly salient (DS) permanent magnet (PM) (DSPM) (PS-DSPM) machines is investigated, in terms of open-circuit flux-linkage, back-EMF, cogging torque, on-load torque characteristics. Analytical deduction shows that by modifying the all poles wound winding to alternate poles wound winding in the 12/11- and 12/13 stator/rotor pole PS-DSPM machines, the fundamental distribution factor and hence the fundamental winding factor can be enhanced, resulting higher torque density. Consequently, among the 12-stator-pole all and alternate poles wound PS-DSPM machines, the 10- and 11-rotor-pole machines exhibit the highest torque density, respectively. However, the 12/10- and 12/14-pole alternate poles wound PS-DSPM machines suffer from higher phase back-EMF even harmonics, resulting larger torque ripple. The 12/10- and 12/11-pole all and alternate poles wound prototypes are built and tested to verify the FE analysis.

Investigation of modular odd-pole PM linear synchronous motors with flux gaps

Purpose – Nowadays, to simplify manufacture process and improve fault-tolerant capability, more and more modular electrical machines are being applied in industrial areas. The purpose of this paper is to investigate a novel modular single-sided flat permanent magnet linear synchronous motor (PMLSM), which adopts segmented armature with the required flux gaps between segments to enhance the performance. Design/methodology/approach – Using 2D finite element analysis, the performances, such as open-flux linkage, back-EMF, average thrust force, thrust ripple, etc., are compared in different values of flux gaps, as well as different slot/pole number combinations (mainly odd numbers of poles). Finally, to show the difference of linear motor from rotary one, the detailed comparison is made between modular PMLSM and rotary PMSM. Findings – Due to flux gaps, it is found the electromagnetic performances are worsened along with flux gap width increasing to modular PMLSMs having slot number higher than pole number, but some aspects of performances such as winding factor, open-circuit flux linkage, back-EMF and average thrust can be improved to those having slot number lower than pole number. Due to the end effect of linear format, the thrust ripple is not significantly improved. Originality/value – It is concluded the proper flux gaps can be chosen to improve the performance of PMLSM with certain slot/pole combinations. A new structure of 12-slot-13-pole (hereinafter referred to as 12s/13p) PMLSM with fractional slot and alternative-teeth wound winding is designed.

Static Characteristics Analysis and Experimental Study of a Novel Axial Field Flux-Switching Permanent Magnet Generator

A novel axial field flux-switching permanent magnet (AFFSPM) machine with a doubly-salient structure is developed as a wind power generator. The electromagnetic characteristics of a 0.6 kW, 3-phase 12/10-pole AFFSPM machine, including the air-gap flux density distribution, open-circuit flux linkage, EMF, and winding inductances, etc., are investigated based on 3-D finite element (FE) analysis. A prototype is built to test the characteristics under both open-circuit and load conditions. The theoretical analysis is validated experimentally. It shows that the phase EMF is essentially sinusoidal, and the machine can not only be used as a wind power generator, but also as a permanent magnet brushless AC motor.